How to label edited images after data augmentation?
Yes, you should label it the same. But more importantly you need to make sure that each perturbation of the image doesn't change some important character of the image. 

Consider training an apple classifier. If you plan to augment data by altering the RGB values, you need to be wary that you might cause issues in classification tasks where color is instrumental. Say, Granny apple / Fuji apple. If you still really want to augment data in this way, consider perturbing by smaller amounts each time.

Or consider an apple detector. An apple still "looks to be an apple" if looked at an angle, if looked through a mirror, if looked afar, but probably not if looked through a carnival mirror.

So ask yourself, if an image still NSFW if the colors are changed?

However, as a personal anecdote I don't think augmenting data by changing the color channel is a good idea. Also note that training on augmented data by altering the color channels as a whole should be more or less equivalent to training in B/W. Why?